When there is a kidney dysfunction, water and waste products that have to be discharged out of body accumulate in blood and imbalance of electrolytes and hormones in the body occurs. Renal failure patients are continuously increasing during last decades, resulting in the significant increase in the national medical expenses and the shortage of medical staffs for renal failure patients.
Most commonly performed to improve such a kidney failure symptom is hemodialysis which is to circulate blood out of body and rid the blood of the accumulated uremic toxin and excess water by a semi-permeable dialysis membrane. Hemodialysis is a method of seeking an electrolyte balance and ridding the body fluid of uremic toxin and excess water, taking advantages of diffusion applied due to the concentration difference and filtration applied due to the pressure difference between blood and dialysate.
For the hemodialysis, a patient visits a hemodialysis center 2-4 times every week and receives hemodialysis treatment which is usually performed for three to six hours. 140 to 200 liters of dialysate is used for each hemodialysis treatment. The dialysate used in the hemodialysis is formed of ultrapure water having no bacteria and virus that can be transmitted to the patient's blood through a hemodialyzer. Thus, a dialysate supply apparatus may include various filtration steps, such as a pre-filtration unit, a water softener, a reverse osmosis filter, and a water sterilization function. Considering that approximately 300 liters of tap water is required to produce 140 liters of reverse osmotic ultrapure water, it is inevitable that a dialysate supply apparatus should be enlarged.
Such in-center hemodialysis occupies more than 80% of entire dialytic therapies. However, it has been reported that the five-year survival rate of renal failure patients on hemodialysis is even below 50%. Hemodialysis patients cannot help following certain dietary restrictions like water control, phosphorus control and protein metabolism. Also, considering a hemodialysis schedule, patients are restricted to leave their community or pursue career and social activities. Ultimately, the quality of life of renal-failure patients on hemodialysis declines hugely.
As a method for overcoming such disadvantages of in-center hemodialysis, much attention has been paid to portable hemodialysis which uses a small and light dialysis device, which can be directly carried or used by a patient. The portable hemodialysis allows patients to receive dialysis treatment when and where they want. In addition, the dialysis treatment can be performed more frequently and the imbalance in the body water level can be corrected more often, alleviating the dietary restrictions. In addition, there are no limits on dialysis places such that patients receiving the portable hemodialysis may travel and move freely enough to improve the quality of their life.
Recent clinical research also shows that daily hemodialysis can reduce cardiovascular complications, increase uremic toxin removal and decrease pre-dialytic uremic toxin levels, which ultimately leads to a lowered mortality risk, as compared with conventional thrice-weekly hemodialysis. As it allows the patient to perform the dialysis in a third place or at home, the portable hemodialysis also contributes for the redistribution of medical staffs necessary for the hemodialysis center. Accordingly, the portable hemodialysis provides various advantages in the patients' social as well as physiological standpoint, compared with the in-center hemodialysis.
Despite such advantages, the portable hemodialysis is performed limitedly because it is difficult for patients to manufacture and manage 140 liters or more of ultrapure dialysate. As mentioned above, considering that more than 300 liters of tap water is required to produce 140-200 liters of ultrapure water, it is practically impossible for patients to produce and manage such a large amount of ultrapure water at home or while traveling. Accordingly, dialysis regeneration draws a great interest because it enables a small amount of dialysate to be continuously reused during hemodialysis. In order to regenerate dialysate, small—(e.g., urea nitrogen, creatinine and phosphoric acid) and middle-sized molecules (e.g., beta 2-microglobulin) are removed from the used dialysate, and pH and conductivity are adjusted. The dialysate regeneration provides various advantages in hemodialysis therapy. The amount of water can be minimized enough to reduce the size of the dialysis device. The cost for hemodialysis may also be reduced, which can eventually reduce financial burdens of the national medical expenditure.
One dialysate regeneration apparatus commercialized is a sorbent filter manufactured by Renal Solutions. The sorbent filter includes four layers for dialysate regeneration, including activated Carbon, Urease, Zirconium Phosphate, and Zirconium Oxide and Zirconium Carbonate. The activated carbon adsorbs and removes diverse sizes of molecules from the dialysate, except urea nitrogen which is a small molecule. Ureases convert the urea nitrogen into ammonia and carbonate ions. Zirconium Phosphate acts as a cation exchanger and removes ammonia, calcium and magnesium ions. On the contrary, Zirconium Oxide and Zirconium Carbonate acts as an anion exchanger to remove phosphate and fluoride. However, the sorbent filter cannot be used together with the citrate anticoagulant which is required for some renal failure patients, because of an aluminum detection problem. Various chemical problems have also been reported.
The dialysate regeneration can also be achieved by physical adsorption performed by an adsorbent, excluding the various chemical bonding described in the sorbent filter. The adsorbent such as the activated charcoal can adsorb diverse sizes of molecules. However, it is known that an adsorption efficiency of the small-sized molecules including urea nitrogen existing largely in the used dialysate is substantially low. However, it has been reported that the adsorption rate of the urea nitrogen by an activated charcoal can be increased by lowering the dialysate temperatures. For example, when a dialysate of 37° C. which is a body temperature is flowing through the activated charcoal, it is identified that 4.5 g of urea nitrogen per 1 kg of activated charcoal is adsorbed. Once the dialysate temperature is lowered to 1° C., the adsorption rate of the urea markedly increases and 11.28 g of urea nitrogen are adsorbed on the same amount of the activated charcoal. Thus, cold dialysate regeneration which uses that the urea nitrogen adsorption is increased at low temperature and the desorption of the urea nitrogen occurs at high temperatures is introduced.
Korean patent application is also published that discloses ‘Cold dialysate regeneration system with carbon and nanofiber column’ (Korean Patent Publication No. 2008-006448) which uses such cold dialysate regeneration. However, there is a big hurdle in the effort to achieve a large variation of the dialysate temperature in the published disclosure because the dialysate temperature is regulated using a Peltier device. In addition, such the patent application has a disadvantage of being a large-sized dialysate regeneration device and cannot pursue the objectives of a small and light-weighted dialysate regeneration apparatus which is essential for the portable hemodialysis.